As a nonvolatile switch used for a memory element or a programmable logic of which semiconductor device circuit configuration can be changed, a switching element utilizing metal ion movement and an electrochemical reaction in an ion conductor (a solid substance in which ions can freely move) is disclosed (see Non-Patent Document 1, for example). This switching element disclosed in Non-Patent Document 1 comprises three layers of an ion conducting layer, a first electrode, and a second electrode. The first and second electrodes abut and sandwich the ion conducting layer. The first electrode serves to supply metal ions to the ion conducting layer. The second electrode does not supply any metal ions. A switching element utilizing such electrochemical reaction is featured by its small size and its large resistance ratio between an on-state and an off-state.
Immediately after manufactured, the switching element utilizing such electrochemical reaction is in an off-state and the resistance thereof is high. To change the switching element from an off-state to an on-state, the first electrode is connected to ground, and a negative voltage is applied to the second electrode. Because of an electrochemical reaction, metal ions are generated from metal of the first electrode and are dissolved in the ion conducting layer. Next, the metal ions in the ion conducting layer are precipitated on a surface of the second electrode as metal. The precipitated metal forms a metal bridge connecting the first electrode and the second electrode. Since this metal bridge electrically connects the first electrode and the second electrode, the switching element is brought in an on-state. On the other hand, to change the switching element from an on-state to an off-state, a positive voltage is applied to the second electrode, while maintaining the connection of the first electrode to ground. As a result, part of the metal bridge is cut off, and the switching element is brought in an off-state.
The switching element utilizing the electrochemical reaction is formed in a multilevel wiring layer structure of a semiconductor device or the like. The switching element includes three layers of a first electrode that can supply metal ions, an ion conducting layer that can conduct metal ions, and a second electrode that is less ionizable (namely, less oxidizable) than the first electrode. Based on the switching element disclosed in Patent Document 1, copper ions are used as the metal ions. In addition, copper is used as the first electrode supplying the copper ions, a metal oxide layer made of tantalum oxide or the like is used as the ion conducting layer, and platinum is used as the less ionizable second electrode.
Patent Document 1:
    Japanese Patent Kokai Publication No. JP-P2006-319028A    Non-Patent Document    Non-Patent Document 1:    Shunichi Kaeriyama et al., “A Nonvolatile Programmable Solid-Electrolyte Nanometer Switch”, IEEE Journal of Solid-State Circuits, Vol.40, No.1, pp.168-176, January 2005.Non-Patent Document 2:    Toshitsugu Sakamoto et al., “A Ta2O5 solid electrolyte switch with improved reliability”, 2007 Symposium on VLSI Technology Digest of Technical Papers, pp.38-39, 2007.